1. Technical Field
The present invention is generally directed to the application of liquid materials. More particularly, the present invention is directed to an air gun for spraying and drying sprayed air-dryable liquid materials such as paints and adhesives.
2. Discussion
Adhesive materials are well-known and have been used since ancient times for providing or promoting adhesion between two articles. Earliest adhesives were based on naturally-occurring substances with little or no processing from their natural forms. Examples of some of these early adhesives include bitumen, fish oil, and certain tree resins. Many adhesives used today are still based on naturally-occurring substances, but have been subjected to processing.
The most notable development in adhesives in recent times has been the use of organic compound-based adhesives. These modern adhesives are based on the synthetic derivation of organic polymers. Solvent-based adhesives have been commonly used in the construction and manufacturing industries.
Typical of these types of adhesives is the "hot-melt" thermoplastic adhesive. Present-day versions of the hot-melt adhesive are composed of polymers such as ethylene-vinyl acetate copolymers, polyamides, polyesters, and polyethylene.
Hot-melt adhesives may be applied in a thick consistency or may be applied as a spray. Devices for spraying heated hot-melt adhesive materials are known. A typical example of such a device is disclosed in U.S. Pat. No. Re. 33,481, issued Dec. 11, 1990, to Ziecker et al. for ADHESIVE SPRAY GUN AND NOZZLE ATTACHMENT. The apparatus of the Ziecker et al. reference is directed to a spray system for spraying heated hot-melt adhesive in elongated strands or fibers in controlled spiral patterns.
In U. S. Pat. No. 5,065,943, issued Nov. 19, 1991, to Boger et al. for NOZZLE CAP FOR AN ADHESIVE DISPENSER a cap adapted for use with an adhesive dispensing device is disclosed. Like the device of Ziecker et al., the Boger et al. device lays down an elongated adhesive fiber onto a substrate in a controlled spiral pattern.
While these devices have utility in providing a method for dispensing solvent-based adhesives, these adhesives themselves are now generally regarded as being undesirable for widespread use. A popular solvent used in these adhesives has historically been trichlorofluoromethane (fluorotrichloromethane) derived from carbon tetrachloride and hydrogen fluoride. While providing very good adhesion, trichlorofluoromethane is now believed to be responsible in part for depletion of the ozone layer. As a result, methylene chloride (dichloromethane) has been more recently substituted for trichlorofluoromethane to overcome the ozone-depletion problem inherent in its use. However, methylene chloride is itself now believed to pose a danger as a carcinogen. It is now apparent that while solvent-based adhesives provide very good adhesion characteristics, their usefulness is severely compromised by their known and suspected dangers to people and the environment.
As a substitute for these adhesives, water-based adhesives have been more recently used. While overcoming the chemical dangers of solvent-based adhesives, the principal difficulty of these adhesives is that they dry very slowly when compared to their solvent-based counterparts, particularly when these adhesives are sprayed onto a substrate. Known systems for applying water-based adhesives that demonstrate an acceptable drying time are wanting.